The present invention relates to collecting spun yarn produced or worked by textile machines to be wound on bobbins. In the industrial production of spun yarns it is common practice for them to be collected on an idle tube carried by a bobbin-carrying arm, which rests on a rotating driving roller and takes up the spun yarn coming from a feed element to wind it onto itself. The bobbin is thus formed by pulling and winding the spun yarn on its surface, it being drawn in rotation by the roller underneath on which the bobbin being formed rests. This practice allows the spun yarn to be wound at a substantially constant linear speed, irrespective of the increasing dimensions of the bobbin and depending only on the rotation speed of said driving roller. The spun yarn is wound in spirals onto the rotating bobbin as the pick-up unit is provided with a thread-guiding device which distributes the spun yarn on the outer surface of the bobbin with backward and forward axial motion. In industry, the bobbins may be shaped like a truncated cone or a straight cylinder with substantially flat bases, with the exception of a few specific cases in which the terminal parts of the bobbins are shaped with a pronounced flare.
In the prevalent industrial use of spun yarn in bobbins, downstream working requires the bobbin to be conical in shape, for example when the spun yarn is unwound in an axial direction from the bobbin fixed on creels. This conicity is however slight and restricted to a few degrees of inclination of the generatrix of the cone in relation to its axis, generally between 2° and 6°, except for some specific uses for which “superconic” bobbins are required.
In the case of winding on a winder the most widespread device for distribution of the spun yarn on the surface of the bobbin with axial backward and forward movement consists of a spiral backward and forward groove cut into the surface of the driving roller which causes the spun yarn to perform an axial excursion of a pre-established length, for a pre-established number of turns of the roller and with a pre-established wind ratio. In other words, the yarn winding and spun yarn distribution elements operate according to a fixed speed ratio.
However, in other cases the device for distribution of the yarn on the bobbin is produced with an independent thread-guiding device, moved by its own driving element, with which the frequency of the backward and forward movement, its travel, the length of the spiral wound and the wind ratio, etc. may be modulated time by time and according to need.
Typically, distribution of the spun yarn on the bobbin with modulatable thread-guide is required in open-end spinning frames, for which distribution of the spun yarn on the bobbin with grooved cylinder does not meet the conditions required for efficacious winding on a bobbin of the desired quality. These winding conditions in particular include its wind ratio, the speed and excursion travel, which cannot be maintained at a single pre-established value, as is the case with the grooved cylinder, but must be adapted time by time to the spun yarn being produced and also modulated during production of the bobbin. There are also other impediments to the use of the grooved cylinder, both due to the geometry of the system and to the overall open-end spinning procedure.
In open-end spinning there is a further limiting condition in that the spun yarn is produced at constant linear speed and therefore must be picked up at a speed corresponding to the speed at which it is made available, substantially equal and constant, maintaining it at a moderate tension, while when forming both straight cylindrical and conical bobbins the pick-up speed typically has a pulsating trend.
It must also be borne in mind that, to compensate these pulsations of adjusting tension and path length, the elasticity of the spun yarn could be taken into account only within the limits of a few per cent, also because the yarn is already stressed considerably at the operating speed of current open-end spinning frames.
To explain more clearly the problems dealt with and the technical solutions proposed with the present invention reference is made, in the description below, to pick-up of “open-end” spun yarns on bobbins, provided purely as a non-limiting example, it being explicitly specified that it may be used advantageously to wind spun yarns produced with different spinning technologies on bobbins.
FIG. 1 show the layout of an open-end spinning station 1 with its most significant components. FIG. 1A shows a front view of it while FIG. 1B shows a side view of it.
Proceeding from the bottom upward, it is first encountered the spinning unit 2 and then the pick-up unit 3, the main components of which used to transform staple parallel fibres into the bobbin of wound spun yarn are illustrated briefly below.
The feed strip or staple S is contained in a cylindrical vessel 4 where it is deposited in a double spiral. The staple S is taken up from this and fed to the unit by a feed roller 5 passing through the condenser/funnel conveyor 6. The strip S then passes to the so-called card 7, a small roller equipped with a toothed seal which rotates at high speed to separate and select the fibres of the staple S and convey then by suction to the spinning rotor 8. In this path the short fibres and impurities are separated, so that only the long and cleanest fibres reach the rotor. The impurities are unloaded in to a suction outlet common to all the spinning units.
In the spinning rotor 8, which rotates at a speed ωR which reaches 150,000 rpm and over, the fibres are deposited in its peripheral groove through centrifugal force; they are then collected and taken up from here in the form of yarn F.
The fibres are delivered axially from the rotor 8 through the opening of the extractor funnel 9, receiving torsions from rotation of said rotor during the path stretching between its inner groove and said extractor 9, to create the plied yarn F.
The yarn is taken up with an extraction system comprising the extraction roller 11 opposite which is an idle pressure roller 12, generally in elastomeric material and pressed with controlled force to grip the yarn F. This extraction roller 11 is operated at controlled speed and determines the spinning speed or the linear production of spun yard in relation to time. The ratio VF/VS between the linear speeds, generally expressed in metres per minute and respectively of yarn extraction and of staple feed with roller 5, determines the drawing ratio between the rotor rotation speed WR and the yarn extraction speed VF in metres per minute determines the number of torsions per metre imparted in the spinning rotor.
To prevent uneven wear, the spun yarn extraction system is equipped with a weft-moving control 13, consisting of an auxiliary thread-guide 14 mounted on a longitudinal rod 15 in common with the other spinning units which moves longitudinally on the front of the machine. The motion of the auxiliary thread-guide 14 is a backward and forward movement with the so-called pilgrim step, for reduced travel, generally below 10 mm, and moves the yarn F crosswise to obtain uniform wear on the pressure roller 12, preventing grooves from forming rapidly on its surface.
The yarn F thus produced is fed to the pick-up unit 3, still moving upwards, and encounters a compensator 16, consisting of a straight or barrel-shaped profile onto which the yarn is diverted to compensate or at least decrease the variations in length of the path stretching between the spinning unit 2 and the point in which the yarn F is deposited on the bobbin, due to the axial motion of the thread-guiding device 20 it follows.
The yarn F therefore reaches the thread-guiding device 20, which distributes the yarn on the bobbin being formed moving crosswise with backward and forward motion. This consists essentially of a main thread-guide 21 mounted on a longitudinal rod 22 common with the other spinning units which moves with alternate motion longitudinally on the front of the machine, with an excursion corresponding to the winding travel on the base tube, generally between 120 and 160 mm.
The excursion frequency required is of 100 to 250 forward and backwards strokes per minute, with position precisions in the order of tenths of mm with regard to the axial coordinate of the inversion points.
In prior art different devices are provided to create, adjust and modulate this alternate motion, in frequency, width and axial shift, in order to obtain bobbins that are stable and good quality. These devices use kinematic systems of the connecting rod/crank, four-bar linkage type and so on. In devices of more recent conception, the rod 22 is moved by a large cylinder cam, not shown in the figure for simplicity, driven to rotate at the controlled speed.
Regulation of the cylinder cam rotation speed allows modification of the frequency of the strokes of the thread-guiding devices 20 and the wind ratio of the spun yarn on the bobbin. A further possibility is also provided of adding a second movement of axial modulation to move the motion inversion point of the thread-guides 21 to decrease phenomena of unevenness at the two ends of the bobbin, distributing them over a greater axial extension.
The thread-guide 21 is extremely near the surface of the bobbin being formed. The bobbin 25 is held by the bobbin-carrying arm 26 provided with two openable idle tailstocks 27 which come into contact with the base tube 28 of the bobbin. The bobbin being formed 25 rests on its driving roller or pick-up roller 29. This pick-up roller is provided with one or more drawing bands 30 in a material with a high friction coefficient, generally rubber. In the case of pick-up on conical bobbins these bands make it possible to establish the drive ratio between bobbin and roller, while in the case of cylindrical bobbins they allow a balanced driving torque to be transmitted to the bobbin 25. The bobbin 25 being formed increases progressively in size and weight. The contact pressure of the bobbin on its pick-up roller 29 has a considerable influence on the density of said bobbin. The contact pressure is therefore controlled with a counterweighing system which acts to keep the contact pressure at a determined value, compensating the effects of its increase.
The use of thread-guiding devices 20 with independent action has noteworthy advantages, such as being able to operate with the exact wind ratio required by the production in progress, to control and avoid ribboning on the bobbin, to obtain stable and well-formed bobbins, but still does not solve all winding problems.
Further problems still encountered in winding spun yarn on a bobbin with distribution by means of independent thread-guiding devices 20 are essentially caused by phenomena, the details of which shall be described below.
One of these concerns distribution of the spun yarn on the generatrix of the bobbin—whether conical or cylindrical—with a thread-guiding means with alternate excursion between the two ends of the winding. This excursion periodically lengthens and shortens the length of the stretch of yarn running between the spinning unit 2 and the point of pick-up on the bobbin 25. This is minimum when the thread-guide is halfway through its travel, and maximum when the thread-guide is at the ends of its travel. This variation therefore causes a first pulsation in the take-up speed of the yarn, as at all times it is necessary to attain from below the algebraic sum of the length of yarn wound on the bobbin with the periodic variation in length—positive and negative—of the path that joins the spinning unit which feeds the yarn F at constant speed and the pick-up element which takes it up a pulsed speed and hence with pulsed tension.
If the bobbin 25 is conical, the phenomena of pick-up speed pulsation is combined with an additional speed pulsation and tension caused by the conical shape of the bobbin. When it is wound on the part of the bobbin 25 with the largest diameter, the yarn F is taken up at a higher speed than the speed at which the yarn F is fed from the spinning unit 2 and is therefore stretched more; instead, when the yarn F is wound on the part of the bobbin with the smallest diameter the situation is reversed: the yarn F is slack as it is taken up at a lower speed than the feed speed of the spinning unit 2.
The average pick-up speed is maintained coinciding with the speed at which the yarn is fed by the rotor 8, or just above this to obtain moderate additional draw and ensure the yarn is always stretched. The overall effect deriving from these tension and speed pulsations on the yarn F being wound is essentially of greater density and compactness of the bobbin 25 in its end points, where tension is greater. The variation in the tension of the yarn F and the consequent more or less dense and compact zones is only partially compensated by the compensator 16, which alleviates the phenomenon but does not eliminate it, and in any case with a certain shift due to the friction of the yarn which runs crosswise on its diverter profile.
A second problem in pick-up of the spun yarn F with the independent thread-guiding device 20 derives from the mass of the thread-guides 21, their rod 22 and their alternate motion control device. The assembly has a significant mass, therefore causing limits to the admissible braking and acceleration values, as well as the minimum braking and acceleration times and spaces. The times and spaces for inversion of motion must in any case come within the order of milliseconds and millimeters respectively, to provide the bobbin with the quality required for the subsequent use, as regards shape and mechanical stability.
In prior art devices which employ the control with cylinder cam and, due to these limits, in the two ends of the stroke where motion is inverted, the profile of the cylinder cam have a smooth radius to avoid impacts, vibrations and damage to the overall system. Consequently, the speed of the thread-guide 21 also has a radiused trend—generally sinusoidal—compared with the axial coordinate while in the remaining part of its stroke the thread-guide is controlled at a constant speed, or at a constant wind ratio. In the end stretches they therefore have a lower average speed and a longer stay time, compared with the intermediate stretch of travel.
The first effect of this longer stay time is that a greater quantity of yarn F is deposited at the two bases of the bobbin, where the yarn being wound is also stretched more tightly. This causes increased compactness at the ends and a further increase in unevenness forming protrusions where the bobbin is already denser. Two harder terminal bulges are formed giving the bobbin an M-shaped profile; this uneven winding causes noteworthy drawbacks in the use and further working of the spun yarn wound on said uneven bobbin.
This winding defect is not permitted for some uses of the spun yarn; in some cases, therefore, the bobbin produced in the open-end spinning frame must be unwound and rewound more evenly with an additional operation and cost.